TAMPA, Fla. (AP) — One way to think about this year's election is as a contest between the impact of a sour economy (advantage Romney) and the power of the nation's shifting demographics (advantage Obama).

Put simply, the groups that support President Barack Obama most strongly — blacks, Hispanics, young people, unmarried women — have been growing as a share of the electorate. Those who support Mitt Romney the most — white working men and older people — have not.

This demographic tide is so strong that some Democrats came away from their 2008 victory feeling that a political reordering was in the works that could be as important as the New Deal realignment that ushered in a generation of Democratic strength after the Great Depression.

The Great Recession put a deep dent in that hope of theirs, as it soured most other optimism around America.

But now both Republicans and Democrats see that the demographic tide is still running. But it is running into the effects of the bad economy.

As Republicans convened here this week, Jeb Bush, the former Florida governor, issued a warning to his fellow Republicans. Perhaps the economic hard times would get them through this year. But soon they would have to face the longer-term implications of America's population shifts.

"Our demographics are changing, and we have to change. Not necessarily our core beliefs, but the tone of our message and the message and the intensity of it for sure," Bush said. "I don't think that's going to have an impact in this election though. . But long-term, conservative principles, if they're to be successful and implemented, there has to be a concerted effort to reach out to a much broader audience than we do today."

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DEMOCRATS ARE hoping Bush is wrong about the impact this year. In fact, it could be said they are hoping the continuing demographic shifts will salvage Obama from the wreckage of the economy.

Charles Cook, one of the country's foremost analysts of election trends, says that basic public opinion about the election has been so stable now for so many months "that the makeup of the electorate is one of the few critical questions."

There are different ways to express the changes that electoral makeup is undergoing.

The percentage of the electorate that is white and not of Hispanic origin has been dropping steadily. It was about 90 percent of the vote in the 1970s. By 2008 it was 74 percent. The white vote has declined an average of 3 points each presidential election since 1992.

Will the trend continue into 2012?

Yes, concludes a study by a liberal think tank that looked at census data in battleground states. The researchers, Ruy Teixeira and John Halpin of the Center for American Progress, combined declines in the white electorate (3 percent) with growth among blacks and Hispanics (2 percent) as well as college-educated whites (1 percent), who are more sympathetic to Democrats than white voters in general. That produced a total swing of 6 percent toward voters more likely to favor Obama.

But demographics are not always destiny. Population trends don't actually register voters or bring them to the polls. The drubbing Democrats took in 2010 was largely explained by the very low turnout among some of their normally loyalist voters. Young voters who helped elect Obama in 2008 stayed away in droves at the midterm. So did blacks and Hispanics

The same thing could happen this year. "Will Democratic apathy and Republican energy make the electorate much more conservative leaning than its underlying demographics would suggest?" Teixera and Halpin asked.

That question is driving both sides, and the effects can be seen everywhere in the presidential campaign.

Just Wednesday, Obama campaigned among University of Virginia students in Charlottesville, one of four college-town appearances he is making in a week to gin up enthusiasm among young voters.

"Go out there, register," he implored the students, "Stand up. If you do, we will win Virginia and if we win Virginia we will win this election and we will finish what we started."

Meantime, Ann Romney went to the Latino Coalition lunch here at the Republican convention, part of a concerted Republican effort to reduce Obama's margins among Hispanics. "I admire your community so much because I know how much you value family and what sacrifices you make for your families," she said.

She stressed the Republican theme that Obama was unsympathetic to small business. "The Latino community is the huge engine of small business," she said, and "they are mistaken if they think they are going to be better off" if Obama is re-elected.

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REVIVING THE economy is an appeal Republicans hope will be heard by all voters, including those who have leaned Democratic. The downturn hit everyone, after all. Pat Mullins, Republican chair in Virginia, said party polling had found that Hispanic voters were less worried about immigration policy than unemployment.

"They're concerned about the same things we are — that their kids have the advantage to better themselves," he said. "That's what they moved here for."

But around the convention there is a palpable subtext, exemplified by Jeb Bush, that just relying on the economic message was a recipe for trouble, certainly in the long term. "We need to start being certain these various communities have leadership roles," Mullins said.

The question of roles sparked some blunt exchanges this week.

The chairman of next week's Democratic National Convention, Los Angeles Mayor Antonio Villaraigosa, took a shot at the Republicans for lining up a string of minority speakers at the opening night of the convention. "You can't just trot out a brown face or a Spanish surname and expect people are going to vote for your party or your candidate," Villaraigosa said.

Indeed, the racial fault lines between the parties are creating conversations that are not always pretty.

A search for black faces at the Republican convention has become a kind of game on Twitter under the hashtag "negrospotting." The pop singer Clay Aiken wrote that he and his brother had been watching and taking a drink each time they spotted a black face and were, as their hashtag put it, "soberasamormon." This prompted the country star John Rich to tweet that Aiken "should be ashamed for racist comments like that."

The Republican Party says delegates aren't asked to identify their race, so they don't know how many are black. The Joint Center for Political and Economic Studies, which has been counting just that since 1974, says there are 46 black delegates, or about 2 percent.

And when it comes to Hispanics, Romney hurt himself during the primaries, particularly when he refused to support Republican Florida Sen. Marco Rubio's legislation to address the problem of young illegal aliens who were brought to the United States by their parents and have lived here for years, gone to school and built lives but remain illegal. Obama then outmaneuvered Romney by unilaterally suspending deportations of these residents.

To counter this, Romney took a step that reflects the very notion Jeb Bush raised — to look at the makeup of the electorate, shape the message and change its intensity. For his speech Thursday evening, the newly minted nominee has chosen someone to introduce him who reflects that changing demographic and can, not coincidentally, help to deliver it: Marco Rubio.

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EDITOR'S NOTE — Michael Oreskes is senior managing editor for U.S. news at The Associated Press. Reach him at moreskes(at)ap.org.